Multi-beam, multi-aperture ion sources of the beam-plasma type

Abstract

A multi-beam, multi-aperture ion source of the beam-plasma type comprises three major regions: the first region where there is created a plurality of electron beams useful for the extraction and focusing of ions; the second region where a gaseous discharge is effected with the aid of the electron beams emerging from the first region, and high frequency oscillation or microwave oscillation is provided by utilization of instability due to electron beam-plasma interactions to thereby create high density ions by that heating energy; and the third region where the electron beams from the second region are collected through the use of a collector, and construction and applied voltage is adjusted to facilitate the high frequency oscillation. The numerous ions created within the second region are trapped into the form of finely focused beams by the well of negative potential which is defined by the plurality of the electron beams emerging from the first region. The resulting ion beams are extracted and combined in a direction opposite to the direction of the electron beams, thereby producing a single well-focused ion beam.

I claim: 
     
       1. A multi-beam, multi-aperture ion source of the beam-plasma type which generates high density ions by utilization of microwave oscillation caused by interactions between electron beams and a plasma, said ion source comprising: housing means defining first, second and third regions, said second region being in mutual communication with said first and third regions;   said first region including a focusing lens system including a plurality of cathodes, a Wehnelt cathode and a multi-apertured anode for generating and emitting a plurality of focused electron beams into said second region;   said second region being defined by an elongated cylindrical drift tube extending the length thereof, communicating at opposite ends with said first and third regions and containing an ionizable gaseous medium at a sufficient pressure for ionization to provide an ionized plasma, said second region further including means for inducing microwave energy oscillations therein to establish wave modes in said plasma which interact with said electron beams and said electron beams traversing the length of said drift tube in a pattern defining a well of negative potential trapping said ions in said second region into focussed ion beams propogating in the opposite direction to said electron beams; and   said third region including a collector plate for receiving and collecting said electron beams from said second region and a source of ionizable material for supplying the latter to said second region;   said high density focussed ion beams being emitted from said second region through the said focussing lens system of said first region simultaneously with and in a direction opposite to the emission of said electron beams.   
     
     
       2. A multi-beam, multi-aperture ion source of the beam-plasma type as described in claim 1, wherein the second region further includes magnet means provided outside said drift tube to provide a magnetic field within the drift tube in the axial direction thereof for focusing said electron beams within said second region and said drift tube and imparting oscillation energy to said plasma. 
     
     
       3. A multi-beam, multi-aperture ion source of the beam-plasma type as defined in claim 1, wherein said ionizable material in said third region comprises metal in gaseous phase. 
     
     
       4. A multi-beam, multi-aperture ion source of the beam-plasma type as defined in claim 1, wherein said collector plate and said drift tube are maintained at a potential difference of between 100 and several hundred volts with said drift tube being maintained at the higher potential such that secondary electrons occurring when said electron beams strike said collector plate are effectively introduced into said drift tube. 
     
     
       5. A multi-beam, multi-aperture ion source of the beam-plasma type as described in claim 1, wherein said third region further includes a second source of electrons for enriching the electron supply in said drift tube.